Html.RouteLink to a Web API Route - possible? - asp.net

Question

My site is largely a suite of web services exposed via the Asp.Net Web API. There are also pages, designed to support the webservices (testing etc), written in Razor (and implicitly Asp.Net MVC 4).
For the XML versions of the webservices I have a schema-export action (uses the XsdDataContractExporter) which is picked up by my standard API route (although note - I've flipped the precedence of the Web API and Pages):
//page routes
routes.MapRoute(
"Default", // Route name
"pages/{controller}/{action}/{id}", // URL with parameters
new { controller = "Home",
action = "Index",
id = UrlParameter.Optional
} // Parameter defaults
);
//an additional route for my Schema controller action
routes.MapHttpRoute("XSD", "schema.xsd",
new { controller = "schema" });
//API Catch-all Route
routes.MapHttpRoute("APIMain", "{controller}/{id}",
new { id = RouteParameter.Optional });
Now on a razor page I want to emit a link to the 'friendly' schema URL ~/Schema.xsd. Anticipating issues with route discovery I immediately went for hitting the route directly by name:
#Html.RouteLink("Schema", "XSD");
However this just emits a link equivalent to ~/.
I've tried some other combinations of route values - but it appears MVC's HtmlHelper and UrlHelper simply don't want to pick up Web API routes.
I'm sure if I cracked open the source of Asp.Net MVC 4 I'd find the reason - but I'm hoping somebody already knows, and since I can't find another SO about such cross-linking I figured it'd be a good addition to the SO library.
I should add that browsing to ~/Schema and ~/Schema.xsd do correctly display the XML schema produced by the API action.

Answer 1

Update
Post-RC a method was added to MVC's UrlHelper, HttpRouteUrl, which does exactly the same thing I suggest here in this answer. This is my discussion thread over on CodePlex where I was told this. So there is no need for you to use the magic string mention here in generating links to Web API routes.
Original answer
I've managed to get it to work - although it might not by the time MVC 4 is RTMd (disclaimer disclaimer!)
I changed my Html.RouteLink call as follows:
#Html.RouteLink("XML request schema", "XSD", new { httproute = true })
I didn't originally intend to answer my own question straight away - but having done some research I found an answer.
First I verified that the HtmlHelper's route collection is the same as the RouteTable.Routes collection (i.e. contained all routes).
Following the call-chain through, I remembered having trawled through the current Web API and page MVC 4 source code from CodePlex, that HttpRoutes (in System.Web.Http.Routing) need a 'hidden' route value to be added otherwise they will never match. Here's the source code from lines 21-25 of HttpRoute class (correct as of 8th June 2012 source):
/// <summary>
/// Key used to signify that a route URL generation request should include HTTP routes (e.g. Web API).
/// If this key is not specified then no HTTP routes will match.
/// </summary>
internal const string HttpRouteKey = "httproute";
A bit of further analysis of the code showed that it expects this route value to be a boolean.
Clearly, this is something that can be turned into extension methods - perhaps Html.HttpRouteLink (and Html.HttpActionLink) - with extra extensions on UrlHelper for hiding the magic string for the route data value.